Due to ongoing issues with google's mail servers (where my perturbee.net mail servers are), I had to switch back to sending mails from this server.
The issues on Google's end were a requirement to log in on their gmail web to fill in a code, then they considered the notification emails too many and limited ability to send from the forum account for spamming. (Response: 550 5.4.5 Daily sending quota exceeded.)

Currently we're sending mails as forum@perturbee.net from this server, which means the mails should arrive, but are likely to be tagged as spam as well.